The present invention relates generally to triggerable spark gap dischargers as protective devices, and specifically to a particular gas mixture which improves the performance of such devices.
Triggerable spark gap dischargers are used as protective devices which have a variety of applications. Exemplary in the art are the systems disclosed in the following U.S. Patents, the disclosure of which are incorporated by reference:
U.S. Pat. No. 3,183,392 issued to Craker;
U.S. Pat. No. 3,387,216 issued to Gagliardi;
U.S. Pat. No. 3,449,156 issued to Tucker;
U.S. Pat. No. 3,786,275 issued to Quesinberry; and
U.S. Pat. No. 4,419,605 issued to Branston.
Mr. Roy E. Wootton describes the protection of klystrons in radar sets in his patent application entitled "Triggered Spark Gap Discharger" Application Ser. No. 06,617,449, filed on 5 June 1984, the disclosure of which is incorporated by reference. Such triggering circuits protect klystrons from damage when a breakdown occurs in the vacuum inside the klystron.
When a breakdown occurs in the klystron, the collapsing voltage appears at the trigger pin of the gas-filled spark gap and causes breakdown of the main gap. This shorts the dc power supply to ground and prevents the energy on the capacitor (several hundred Joules) from damaging the klystron. Because the voltage on the main-gap of the spark gap is falling at the time the trigger gap fires, it is important that the spark gap works effectively at the lower end of its operating range. This range should be as wide as possible, and the gap should be able to respond to as wide a range of trigger voltage amplitudes as possible.
An example of the current operating range produced by protective circuits using spark gaps, is the range of 19-22 kv when pure nitrogen N.sub.2 is selected as the gas to fill the gaps. Such triggering behavior is typical of commercial triggerable spark gap circuits. However, note that higher or lower voltages outside the operating range will not fire the main gap, even though the trigger gap may briefly fire with the higher trigger voltages.
This type of undesirable behavior occurs for gaps filled with a variety of gases and mixtures. It also is known to occur with both new and aged spark gaps, and variations of trigger electrode and insulator geometry.
From the foregoing discussion, it is apparent that there currently exists the need to expand the operating range of triggerable spark gap protective circuits. The present invention is intended to satisfy that need.